Foamed cellulose tobacco filter rod

ABSTRACT

A cylindrical rod particularly suitable as a cigarette filter is described which is comprised predominantly of foamed fibrous cellulose and a water-insoluble polymer having a glass transition temperature of at most 50* C. and a minor amount of wetting agent, the weight ratio of the polymer to the fibrous cellulose being at least about 0.4, said rod being encased by a skin of said polymer.

United States Patent [72] Inventors Saunders E. Jamison Summit; Gene 11. Anthony, Whitehouse Station, NJ. [21] Appl. No. 562,095 [22] Filed July 1,1966 [45] Patented Jan. 12,1971 [73] Assignee Celanese Corporation 1 New York, N.Y.. a corporation of Delaware [54] FOAMED CELLULOSE TOBACCO FILTER ROD Primary Examiner-Melvin D. Rein Attorneys-W. J. Mason, S. D. Murphy and Leonard Horn ABSTRACT: A cylindrical rod particularly suitable as a cigarette filter is described which is comprised predominantly of foamed fibrous cellulose and a water-insoluble polymer having a glass transition temperature of at most 50 C. and a minor amount of wetting agent, the weight ratio of the polymer to the fibrous cellulose being at least about 0.4, said rod being encased by a skin of said polymer.

FOAMED CELLULOSE TOBACCO FILTER ROD This invention relates to the preparation of stable cylindrical rods of foam cellulose encased by a rigid skin. More particularly, it is concerned with the manufacture of improved filters for cigarettes and improved tampons.

The cellulose foam filters described in application Ser. No. 444,104 filed Mar. 29, 1965 now abandoned, have many advantages over prior art cigarette filters. However, one difficulty with them has been their relatively poor firmness retention during the smoking of the attached cigarette. Tobacco smoke contains a significant amount of moisture such that a cigarette filtertends to lose its firmness during'the' course of smoking. Such a loss of firmness is of course objectionable to the filter cigarette-smoking public. Moreover," previous methods of forming the requisite rod shape and dimensions have serious disadvantages from the point of view of time, cost and/or the product quality; For example, in'the aforesaid application, Ser. No. 444,104 the cellulose foam is drained and poured into molds and allowed to dry. Pouringinto small tubes is a slow, tedious, costly process. The foam must be plugged, drained for a long period, dried, removed and compressed considerably. On the other hand, if the foam is cast in large sheets and dried and the filter rod is cut therefrom, someof the cellulose foam is wasted and more importantly, any rigid skin formed by the polymeric binder is lost. Furthermore, significant amounts of the polymeric binder drain off thus representing a loss of relatively expensive starting material.

It is an object of this invention 'to produce cigarette filter rods which will retain a high level of firmness during smoking.

The structure disclosed is capable ofo'ther uses, for example, as a tampon in which it is possible to absorb up to about 15 times its weight of water. The filter is made by mixing fibrous cellulose, wetting agent and certain water-insoluble resins in water and expanding the slurry to a foam by agitation. The foam, without draining, is then extruded through a cylindrical tube and is deposited on a receiving surface in the form of wet, soft cylindrical units, and then dried.

The concentration of materials in the slurry .is critical toward realizing the advantages of this invention. The woodpulp, or other cellulose fiber source, should constitute about 9 to 13 percent, the wetting agent about 0.2 to 2 percent, the water-insoluble resin about 5 to percent and about 80 to 84 percent water. (All parts mentioned in this specification are by weight unless otherwise stated.) The weight ratio of waterinsoluble resin to fibrous cellulose in the final product should be about 0.4 or greater. v i

The fibrous cellulose starting material is conveniently prepared from refined wo'odpulp' having at least a moderate alpha cellulose content, i.e., at least about 75 percent. if the alpha cellulose content is too low, the woody flavors" of lignin are tasted by the smoker. Cotton linters represent another good source. The fiber length is advantageously less than onehalf inch, and desirably less than one-fourth inch. Longer fibers are more difficult to disperse but may be present in small amounts (c.g. about 1 to 10 percent) to add strength.

The water-insoluble resin should be one which has the ability to form a continuous film at relatively low temperatures upon the evaporation of water. The resin should have a glass transition temperature of 50 C. or less.'Tables of glass transi tion temperature factors are readily available so that the glass readily ascertainable' theoretical limit for determining whether a polymer or copolymer is within the scope of the invention.

Homopolymers or copolymers can be employed. Exemplary of suitable resins are polyvinylacetate, polyvinylidene chloride, polybutyl acrylate and cross-linkable acrylics. Homopolymers of vinylchloridc, styrene and acrylonitrile are not suitable resins for this invention, however copolymers in which these monomers are included and which have a suitable transition temperature of copolymers based on the percent constituent monomers can readily be ascertained by adding the temperature factors of each constituent corresponding to its percentage in the copolymer. For example the glass (transi- & Haas Acrylic Glass Temperature Analyzer by adding together the corresponding temperature factors, 1.46, 1.59 and 0.17, respectively, to yield a net temperature factor of 3.22 which corresponds to a glass temperature of 38C. The

minimum film-forming temperature '(M.F.T.) is slightly lower than the glass transition temperature due to the presence of impurities. Thus the glass transition temperature representsa low glass transition temperature are utilizable. Numerous commercial formulations are available. it is necessary, of course, for end uses of the foam cellulose rods which involve significant contact with the human body, that the resin be physiologically harmless.

Polyvinyl acetate homopolymer is the preferred water-insoluble resin. The polyvinylacetate advantageously is of high molecular weight, having an inherent viscosity (measured in standard manner using a 0.4 percent solution of the polymer in aqueous percent acetic acid at 25 C.) in the order of about 1.1-1.3.

It has been further discovered that the smoothness of the exterior surface of the drying filter rods critically depends on choice of wetting agent. Nonionic wetting agents such as saponin and lauric diethanolamide give the best results. Less preferred wetting agents are the cationic ones such as the quaternary ammonium halides, for example cetyltrimethylammonium bromide. Still less preferred are the anionic wetting agents such as sodium lauryl sulfate and dodecylbenzene sodium sulfonate. When these latter wetting agents are used, the exterior of the rod has so many indentations that it cannot be effectively used as a commercial cigarette filter. The wetting agent should of course be compatible with the other ingredients and should have the property of forming relatively stable bubbles or foam in their presence.

The foam, produced in the conventional manner by agitation, is transferred without provision for drainage to the extruding apparatus. It is then extruded through a cylindrical tube and onto a wet surface in the form of a wet cylindrical rod. This rod is surprisingly stable and is self supporting and in contact with the foreign surface only tangentially at its bottom support. The wet rod is then dried in-an oven to remove the water by evaporation. Upon cooling, the water-insoluble resin concentrates to give a firm structure with much of the resin wicking to the surface to give a firm casing to the porous rod in the form of a rigid skin. Any minor deviation of the rod from circular cross section can be readily corrected by rolling between heated metal plates either about midway in the drying period or after the drying. The rigid skin of this filter rod leads to a high firmness retention; The process of this invention is illustrated in the following embodiment.

EXAMPLE ,The following ingredients are introduced into a l-quart Waring Blender: 20 grams acetate-grade woodpulp, 30 grams polyvinylacetate homopolymer emulsion (55 percent solids), 3 grams of saponin and 135 milliliters of water.

The pulp, previously shredded by hand,fwas slowly added to and dispersed in the mixture of emulsion and water. When a smooth, thick slurry was achieved, the rate of agitation was increased to produce a foam volume of 400 milliliters. The foam was then transferred to a cylindrical vchamber to which a pipe of 1 centimeter in diameter, l-inch long, is attached. The foam was forced through this pipe by means of a plunger applied by hand from the opposite end of the cylinder. The cylinder of foam issuing from the pipe was deposited on a sheet of Teflon which was placed in an oven at 120C. After a drying period of about 45 minutes, the rods were removed from the sheet,

rolled between aluminum plates at C. and allowed to cool. The rods were then wrapped in cigarette paper with the Ajusta-Betta Cigarette Roller and cut into 2 centimeter filter ters in nine, 2-second puffs of 35 milliliters at 1-minute intervals. After smoking, the reduction in diameter of these tips under a l-pound load was about 20 percent. Commercial acetate filter tips are compressed about 20-25 percent under The stable foam cellulose rods of this invention can also be employed as tampons. i.e. inserted into body cavities. They have a smooth exterior and are nonabrasive. Due to the nature of the instant inventive process, the rod diameter can readily asimilar test whereas the cellulose foam filter tips prepared as 5 d pensively be adjusted to rneet varying size requiredescribed in the aforesaid application Ser. No. 444,104 are merits merely y regblatmg the dlametel' of the extrusion compressed about) percemundel- Suchatest cylinder. Where swelling of the tampon is not desired, the

Table I further illustrates the excellent results obtainable foamed oelhflose rod as ep o e be directly usedemploying the method of the instant invention. Filters where swelbllg ofthe tampon l3 deslfed, as for example prepared in accordance with the instant invention (samples 1- to afforo a tlgbtel' fit, the above'prodbeed Tod can be 6 are compared with filters prepared without observing mersed m water e {town and dried at up to about one the critical concentrations of this invention (samples 7 and 8) tenth to one fifth of mama] Y l when thus P X and filters prepared in accordance with example 30f applicat tampon expands up to ongmal volume upon absorbmg tion Ser. No. 444,104 (sample 9) and also commercial filters hquld' f a commercial cigarette brand (sample 10 Numerous variants of the above-described foamed cellulose in sample 9the PVAc/pulp ratio in the initial foam composirods f Ptooesses b manufacture be PP o to tion is significantly different from aid ti i h d i d one skilled in the art within the scope of the present invention. product due to the loss of polyvinylacetate during drainage. We cla1m: The two sets of values for sample 9 correspond to two dif- A y ri tobacco Smoke filter rod COmPHSCd ferent filter tips prepared from the dried foam. Firmness was predommantly of a physical admixture of foamed fibrous celagain determined as the percentage of the original diameter of lulose and water-Insoluble; P y bevmg a glass transltton the filter retained on application of a l-pound load. The tip temperature o at o 50 abd a minor amount of wetting weight is included to show that the weight of the filter tips of e the Welgbt of e p y e to the fibrous eenblose this invention are comparable to those of present commercial e at least about sold rod bemg encased y a 5km of filter tips. Sold P y TABLE I Initial foam composition, Filter tip,

weight percent firmness, percent Pressure Wetting PVAc/ Before After drop, Tip agent Water Pulp PVAc pulp smoking smoking mm. H2O wt.,g.

l0. 5 5. 5 52 93 83 32 0. 135 11 6 .55 92 75 33 0.140 12 6 60 89 73 24 0. 138 10 5 .50 91 83 35 0.147 13 5 38 89 80 36 0. 148 10 8 80 93 82 34 0. 164 11. 5 3. 5 90 66 41 0. 133 14 7 50 92 71 29 0.147 3.3 2.8 .85 so 55 0. 09 87 11. 5 10 86 61 45 0. 10 10 80 73 65 0. 14

2 A tobacco smoke filter according to claim 1 wherein the water-insoluble polymer is vinylacetate homopolymer.

3. A tobacco smoke filter according to claim 1 wherein the wetting agent is saponin. 

2. A tobacco smoke filter according to claim 1 wherein the water-insoluble polymer is vinylacetate homopolymer.
 3. A tobacco smoke filter according to claim 1 wherein the wetting agent is saponin. 